The present invention relates to method and apparatus for one-time or continuous nondestructive determination of the penetration and leaching process of conductive phases in materials.
The determination of the penetration depth of a liquid phase in porous materials plays an important part, primarily in the so-called water impermeability tests of concrete samples. The only testing method known so far, and defined in DIN-Standard 1048, Part I (German Industrial Standard), for the determination of the penetration depth of water in concrete is based on the splitting of a test body according to defined charging conditions, and visual evaluation of the moisture penetration depth at the break surface. The same method is also employed to examine the penetration and leaching behavior of salt solutions in concrete to test suitable concrete mixtures for the storage of radioactive wastes in salt domes (see, for example, R. Wendehorst, Baustoffkunde (Construction Materials), published by C. R. Vincentz Verlag, Hannover 1975, and G. Franz, Beton Kalendar (Concrete Calendar) 1980, Part II, published by W. Ernst & Sohn, Berlin, 1980 and Verein Deutsche Zementwerke, Zement Taschenbuch [Cement Handbook] 79/80, published by Bauverlag, Wiesbaden, 1980).
This testing method has considerable drawbacks. It harbors a large inaccuracy component which is produced mainly by the visual evaluation of the moisture penetration depth at the split surface of the sample body. This applies particularly in the case of solutions, since the dissolved substance and the solvent exhibit different penetration behaviors. In leaching tests there exists an additional difficulty that visible fronts do not appear at all and slight gradual differences cannot be detected. Moreover, the sample body is destroyed. This necessary splitting of the sample body makes it unusable for further measurements. Continuous measurements and long-term observations, e.g., stability of impregnations and coatings, are therefore impossible. Moreover, discontinuities during the penetration and leaching process cannot be detected. Finally, the regular monitoring of already installed components or instorage concrete shieldings cannot be performed. This is of significance particularly, for example, in the permanent storage of radioactive wastes where under certain circumstances certain changes may take place in the interior of the shielding material.
However, such information has great significance in connection with the storage of radioactive wastes. On the one hand, storage barrels or drums are encased in a concrete shield which, upon storage in a salt dome, may be exposed to a salt solution if there is a water break-in. Additionally, it is necessary, on the one hand, to test concrete mixtures which are highly resistant to the penetration of the solution while, on the other hand, long-term changes in the permeability of the shielding material must be able to be monitored.
Additionally, liquid radioactive wastes are sometimes incorporated in a cement mixture for permanent storage. In such case, the leaching behavior of these substances must be tested and monitored.
In the construction industry as well, knowledge of the transport of moisture and salts in construction materials is of great importance because these factors decisively determine the durability of the material and the setting of a defined microclimate within the enclosed area of the structure. Changes in these properties due to the use of paints and sealers also play a significant role here.
Finally, in road construction, potholes are ascribed primarily to water vapor which in winter rises from lower layers and is condensed and frozen in the upper roadway coating. Efforts are therefore continuing to find materials for the cover layer which are substantially impermeable to water vapor diffusions.